1. Technical Field
The present invention relates to an optical scanning device, an optical scanning display device and an optical scanning method.
2. Related Art
Various types of optical scanning devices have been proposed so far, such as a raster scanner disclosed in Hakan Urey, Randy Sprague, “Biaxial MEMS Raster Scanner with Linear Ramp Drive”, Optical MEMS 2003, IEEE-LEOS, Waikoloa, Hawaii, August 2003, teachings of which are incorporated herein by reference. The raster scanner is designed to scan incident light according to an oscillating action of a scanning mirror. In the raster scanner, a vertical scanning signal employed for vertical scanning is made up of sawtooth waves. Thus, the vertical scanning signal rises from its minimum level to its maximum level linearly with the passage of vertical scanning time and thereafter returns instantly to the minimum level in each cycle. As above, the scanning mirror in a raster scanner oscillates according to the aforementioned change in the level of the vertical scanning signal.
However, in the raster scanner described above, a rebound occurs to the scanning mirror when the vertical scanning signal instantly returns from the maximum level to the minimum level during the oscillating process of the scanning mirror according to the level change of the vertical scanning signal.
Since the scanning mirror is generally supported with respect to the scanning devise via an elastic beam member so as to allow for the oscillation of the scanning mirror. Therefore, each raster scanner has an intrinsic resonance frequency which is determined by the configuration of the scanning mirror and characteristics of the elastic beam member.
Therefore, when the resonance frequency of the raster scanner is included in frequencies caused by the rebound, resonant vibration occurs to the scanning mirror. Due to the resonant vibration, the scanning mirror becomes incapable of following the level change of the vertical scanning signal after the aforementioned return, by which a pulsating motion of the scanning mirror (differing from the level change of the vertical scanning signal) is caused. As a result, the vertical scanning of the incident light can not be conducted desirably.
The present invention is advantageous in that an improved optical scanning device, an optical scanning display device and/or an optical scanning method are provided, that are configured to form a scanning signal having a waveform elaborately designed by making effective use of a sawtooth wave and to excellently carry out the scanning of light by use of the scanning signal.
In accordance with an aspect of the present invention, there is provided an optical scanning device having a scanning element including an oscillating member which is elastically supported to be capable of oscillating, scanning signal generating unit which generates a scanning signal within a predetermined period, the scanning signal including a sawtooth wave part and a corrective wave part which is formed based on an intrinsic resonance frequency of the scanning element, to suppress the resonance vibration of and driving means which drives the oscillating member to oscillate it according to the generated scanning signal.
In the optical scanning device configured as above, when the corrective wave part is formed to suppress the resonance vibration of the scanning element based on the intrinsic resonance frequency of the scanning element, the resonance vibration of the scanning element (executing the scanning according to the sawtooth wave part included in the scanning signal) is effectively suppressed by the corrective wave part. Consequently, the scanning by the scanning element can be carried out excellently.
In accordance with another aspect of the present invention, there is provided an image display device, which is provided with a beam emitting unit which emits a beam carrying image information, a horizontal scanning unit which horizontally scans the beam emitted by the beam emitting unit, a vertical scanning unit which vertically scans the beam scanned by the horizontally scanned unit. At least one of the horizontal scanning unit and the vertical scanning unit is implemented by an optical scanning device which includes the scanning device described above.
In accordance with a further aspect of the invention, there is provided a method for driving a scanning unit including an oscillating element which is elastically supported to be capable of oscillating, which includes the steps of generating a driving signal including a sawtooth wave part and a corrective wave part which is formed based on a resonance frequency intrinsic to the scanning unit, within a predetermined period, and driving the scanning unit in accordance with the driving signal.
In the optical scanning device, image display device, and method for driving a scanning unit configured as above, since the resonance of the scanning element is suppressed by the corrective wave part, the scanning can be carried out excellently.